Modal based stability analysis of power systems using energy functions

In this paper a physically based decomposition technique is exploited to perform direct stability analysis of power systems using the energy function method. The slow-coherency analysis decomposes the system into r areas associated with (r- 1) slow modes of the linearized system. The centres of inertia (COIs) of these areas from the slow subsystem and the rest of the fast modes are associated with different areas. The system transient energy function E is decomposed into E_slow associated with the slow variables of the slow subsystem, E_fast associated with the fast variables of the r-areas and E_fast-slow which is a function of both fast and slow variables. Depending on the fault location and strength of connection between areas, the sum of E_slow, E_fast-slow and E_fast of the disturbed arease constitutes a good approximation to the system energy function. Using this partial E-function and the potential energy boundary surface (PEBS) method, both E_cr and t_cr are computed. Numerical results on a 10-machine 39-bus system are presented in support of the technique.